1. Field of the Invention
The present invention relates to a method and apparatus for detecting a touch position, and a touchscreen display apparatus having the apparatus. More particularly, the present invention relates to a method and apparatus for detecting a touch position having a substantially enhanced touch position detecting capability, and a touchscreen display apparatus having the apparatus.
2. Description of the Related Art
Generally, a touch panel is included on an upper portion of a liquid crystal display (“LCD”) device to enable a user to select information displayed on a screen of the LCD device by making contact with a finger or an object, such as a stylus, for example. The touch panel detects a touch position at which the finger or the object makes contact with the screen, and transforms sensed contact information corresponding to the touch position into an input signal to be utilized by the LCD device. The touch panel typically includes a first substrate, a second substrate spaced apart from the first substrate by a predetermined distance, a first transparent electrode disposed on the first substrate, and a second transparent electrode disposed on the second substrate. The first electrode and the second electrode face each other, and a liquid crystal layer is interposed between the first substrate and the second substrate.
When a computer includes the LCD device having the touch panel, an additional input apparatus such as a keyboard or a mouse, for example, is not necessary. Thus, the touch panel is widely used.
When the touch panel is disposed on an LCD panel of the LCD device, however, a thickness and size of the LCD device having the touch panel is increased. Thus, to decrease the thickness and size of the LCD device having the touch panel, the touch panel may be integrally formed with the LCD device.
The LCD device may include a photo sensor which detects a shadow formed by the finger or the object blocking light when touching the touch panel or the photo sensor may detect additional light generated from a light pen touching the touch panel. A readout voltage detected from the touch panel is compared with a reference voltage by a comparator to determine a touch state of the LCD device. More specifically, the touch state is determined by the discriminator when the readout voltage is greater than the reference voltage, and a non-touch state is determined by the discriminator when the readout voltage is less than or equal to the reference voltage, for example.
However, the reference voltage is a fixed voltage, and a mis-touch discrimination operation occurs as a result. More particularly, when a reference voltage having a relatively high level is used in a touch discrimination operation, normal touch discrimination may be performed. However, when reference voltage having relatively low level is used in the touch discrimination operation, many or all points on the touch panel may be determined to be a touch state, thereby degrading an accuracy of the touch discrimination operation.
Additionally, a variation of the readout voltage is caused by various factors such as a threshold voltage of a transistor and a sensor gap variation. Moreover, a threshold voltage shift of the transistor due to a current flowing in the transistor, as well as a temperature dependence of a liquid crystal capacitor, further cause a drift of the readout voltage. Therefore, the accuracy of the touch discrimination operation is further degraded, and a touch state is thereby mis-determined.